Improved operation of a refrigerant system

ABSTRACT

A method and system for operating a refrigerant system having a reciprocating compressor with a main cylinder module and an economizer cylinder module includes regulating a flow of refrigerant into the main cylinder module and regulating a flow of refrigerant into the economizer cylinder module. The main cylinder module and the economizer cylinder module have separate inlet and outlet discharge streams. The flow through each module is regulated as a function of an operating mode of the refrigerant system, which includes various modes of loading and unloading based, in part, on a cooling demand. In some embodiments, the refrigerant system may include a connector refrigerant line configured to redirect refrigerant from the economizer cylinder module to the main cylinder module or from the main cylinder module to the economizer cylinder module.

FIELD OF THE INVENTION

The present invention relates to a refrigerant system having an economizer module and a reciprocating compressor. More particularly, the present invention relates to a method and system for operating the refrigerant system in various modes of loading and unloading.

BACKGROUND

Refrigerant systems are used to condition air in an environment by controlling the temperature and/or the humidity of the air. In a typical air conditioning or refrigeration system, a compressor delivers a compressed refrigerant to an outdoor high pressure heat exchanger, known as a condenser or a gas cooler. If the refrigerant in the outdoor heat exchanger, when cooled, condenses into a liquid this heat exchanger is commonly referred to as a condenser. If the refrigerant exiting the compressor is at a thermodynamic state above critical point, then the refrigerant upon cooling in the heat exchanger may not condense into a liquid but would simply be cooled to a lower temperature. In this case, this heat exchanger is commonly referred to as a gas cooler. From the high pressure heat exchanger, the refrigerant passes through an expansion device, and then to an indoor heat exchanger, known as an evaporator. In the evaporator, the air is blown over the evaporator external surfaces to lower a temperature of the air, and moisture may also be removed from the air to lower its humidity. From the evaporator, the refrigerant is returned back to the compressor.

An economizer cycle may be used in a refrigerant system to increase the capacity and efficiency of the system. When the economizer cycle is actuated, a portion of the refrigerant is tapped from a main refrigerant circuit at a position downstream of the high pressure heat exchanger. The tapped refrigerant is expanded to a lower intermediate pressure and temperature, at which point it passes through an economizer module, which is commonly called an economizer heat exchanger, to further cool high pressure refrigerant in the main refrigerant circuit. The tapped refrigerant is returned back to the compressor, typically at an intermediate pressure. The main refrigerant travels to the evaporator where it has a greater thermodynamic cooling potential (cooling capacity), due to the fact that it has been additionally cooled in the economizer heat exchanger. An economizer cycle can also be achieved through the use of a flash tank, instead of the economizer heat exchanger, as known in the art.

In one design, the refrigerant system may use a reciprocating compressor having two separate sets of cylinder modules, which are configured to receive and compress two separate refrigerant streams. An economizer cylinder module may be used to compress the tapped refrigerant from the economizer module, whereas a main cylinder module may be configured for compressing the main refrigerant from the evaporator. Downstream of the compressor, the two refrigerant streams may be combined before flowing back to the high pressure heat exchanger.

During operation of the refrigerant system, there may be conditions in which it is ineffective to use the economizer cycle, even though the refrigerant system is operating at or near full load. For example, if the ambient air temperature is high and the suction pressure entering the compressor is also high then the economizer cycle engagement may not add any additional cooling and thus the economizer cycle may be disengaged, even if there is a high cooling demand (i.e. full load). At other times, it may be beneficial to operate a refrigerant system in a mode that limits the cooling capacity by limiting a flow of refrigerant through the system, which may be referred to as unloading. The unloading can be achieved by disengaging the economizer circuit or providing by-pass operation. There is a need for improved flexibility to vary a cooling capacity for a refrigerant system having an economizer cycle and a reciprocating compressor with a dedicated economizer cylinder module.

SUMMARY

A method and system is described herein for operating a refrigerant system having a reciprocating compressor with a main cylinder module and an economizer cylinder module. In the context of this application a single cylinder module may be substituted by bank of cylinders modules. The refrigerant system provides cooling by circulating a refrigerant through a high pressure heat exchanger, an economizer module, an evaporator, and at least one of the main cylinder modules and at least one of the economizer cylinder modules. The main cylinder module and the economizer cylinder module have separate inlet and outlet streams. The flow of refrigerant into the main cylinder module may be controlled as a function of an operating mode of the refrigerant system, which includes various modes of loading and unloading based, in part, on a cooling demand. The flow of refrigerant into the economizer cylinder module may separately be controlled as a function of the operating mode. In some embodiments, the refrigerant system may include a connector line configured to redirect refrigerant from the economizer cylinder module to the main cylinder module or from the main cylinder module to the economizer cylinder module.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a refrigerant system including an economizer module, a reciprocating compressor having a first inlet connected to a main refrigerant line and a second inlet connected to an economizer refrigerant line, a first valve in the main refrigerant line, and a second valve in the economizer refrigerant line.

FIG. 2 is a schematic of an alternative embodiment of the refrigerant system from FIG. 1, and includes a connector line and corresponding valve between the main refrigerant line and the economizer refrigerant line.

FIG. 3 is a schematic of a flash tank that may be used in the economizer module as an alternative to an economizer heat exchanger.

DETAILED DESCRIPTION

FIG. 1 is a schematic of refrigerant system 10 including compressor 12, high pressure heat exchanger 14, first expansion device 16, economizer module 18, second expansion device 20, evaporator 22, first valve 24, second valve 26 and controller 28. Refrigerant system 10 is configured to circulate a refrigerant through system 10 to provide cooling and condition an air stream (not shown) passing through evaporator 22.

Compressor 12 is a reciprocating compressor and includes main cylinder module 30 and economizer cylinder module 32. It is recognized that one or both of main cylinder module 30 and economizer cylinder module 32 may include more than one cylinder and more than one cylinder module. In an exemplary embodiment, main cylinder module 30 has higher displacement than economizer cylinder module 32. Compressor 12 includes first suction inlet 34, which is connected to main cylinder module 30, and second suction inlet 36, which is connected to economizer cylinder module 32. Similarly, compressor 12 also includes first discharge outlet 38 extending from main cylinder module 30 and second discharge outlet 40 extending from economizer cylinder module 32. System 10 is designed such that main cylinder module 30 and economizer cylinder module 32 each receive a distinct refrigerant stream for compression. As shown in FIG. 1, main cylinder module 30 is configured to receive refrigerant from evaporator 22 and economizer cylinder module 32 is configured to receive refrigerant from economizer module 18.

Two refrigerant streams exit compressor 12 via first outlet 38 and second outlet 40 respectively. Before entering high pressure heat exchanger 14, the refrigerant streams are recombined such that high pressure heat exchanger 14 receives one refrigerant stream. In high pressure heat exchanger 14 operating as a condenser, the vapor refrigerant condenses to form liquid refrigerant. In an alternative embodiment of refrigerant system 10, high pressure heat exchanger 14 may be substituted with a gas cooler, where refrigerant stays in a single phase thermodynamic state.

Once the refrigerant exits high pressure heat exchanger 14, the refrigerant may again be split into two refrigerant streams. A main refrigerant stream flows through main refrigerant line 42 a; an economizer refrigerant stream flows through tap line 44 a, also referred to as economizer refrigerant line 44 a. The refrigerant in tap refrigerant line 44 a passes through first expansion device 16 in order to lower its temperature and pressure before passing through economizer module 18. Expansion device 16, as well as second expansion device 20, may include a capillary tube, an orifice, a thermostatic expansion device, or an electronic expansion device.

Inside economizer module 18, the refrigerant flowing through tap line 44 a further decreases a temperature of the main refrigerant stream passing through main refrigerant line 42 a. Economizer module 18 is used to provide additional cooling capacity to the main refrigerant stream. In an exemplary embodiment, economizer module 18 is a heat exchanger. An alternative embodiment of module 18 is described in further detail below. Also, as known, the economizer refrigerant flow may be tapped downstream (instead of upstream) of economizer module 18. Such system configurations are within the scope and can equally benefit from the invention.

After exiting economizer module 18, the main refrigerant stream passes through second expansion device 20, and then to evaporator 22 through main refrigerant line 42 b. The main refrigerant is evaporated inside evaporator 22 by removing heat from air passing over external surfaces of evaporator 22. Main refrigerant line 42 c connects evaporator 22 to inlet 34 of main cylinder module 30, and the refrigerant flows through main refrigerant line 42 c to undergo compression in a separate compression path in the main cylinder module 30. First valve 24 is located in main refrigerant line 42 c and regulates a flow of the main refrigerant between evaporator 22 and compressor 12. The economizer refrigerant stream flows directly from economizer module 18 to compressor 12 through economizer refrigerant line 44 b. Second valve 26 is located in economizer line 44 b and regulates a flow of the economizer refrigerant between economizer module 18 and compressor 12. More specifically, economizer refrigerant line 44 b connects to second inlet 36 of compressor 12.

The present invention includes the use of valves 24 and 26 to control a flow of refrigerant into compressor 12, and more specifically to control a flow of refrigerant through main cylinder module 30 and economizer cylinder module 32. An amount of cooling provided by refrigerant system 10 may be controlled by controlling a circulation of the refrigerant through main cylinder module 30 and economizer cylinder module 32, as described further below. A cooling capacity of refrigerant system 10 may be varied by operating the system in loading or unloading modes. These operational modes are also described in further detail below.

Valve 24 is used to control the flow of refrigerant into main cylinder module 30, which directly impacts an amount of cooling provided by evaporator 22. As more refrigerant is pumped through cylinder module 30, more refrigerant is circulated through evaporator 22, which results in increased amount of cooling of air passing over the evaporator 22. Similarly, valve 26 controls flow of refrigerant through economizer cylinder module 32. As more refrigerant is pumped through cylinder module 32, more refrigerant is circulated through economizer module 18, which provides additional cooling to the refrigerant in main refrigerant line. As described below, valves 24 and 26 are controlled in order to regulate an amount of cooling provided in evaporator 22.

For a refrigerant system similar to system 10, but not including valves 24 and 26, unloading may not be possible, or be very limited, without essentially shutting down system 10, which may be undesirable for several reasons. In refrigerant system 10 of FIG. 1, three levels of unloading are made feasible by valves 24 and 26. Refrigerant system 10 is able to operate in four different operating modes shown in Table 1 below, depending on a position of valves 24 and 26.

TABLE 1 Operating First Second Mode Valve 24 Valve 26 Comments Full loading Open Open Typical for high pressure ratio. with Would be identical if valves 24 economizer and 26 are not present in system Mid-level Open Closed Economizer cycle blocked unloading Full Closed Open Unloading with discharge flow unloading A cooling Full Closed Closed Unloading without discharge unloading B flow cooling

In the scenario in which both valves 24 and 26 are open (i.e. full loading with economizer), refrigerant system 10 operates the same as a refrigerant system not having valves 24 and 26 for controlling refrigerant flow into the reciprocating compressor 12. In the full loading mode of Table 1, the economizer cycle is being utilized since valve 26 is open. In the economizer mode, economizer module 18 uses refrigerant in the tapped refrigerant line 44 a to further cool refrigerant in the main refrigerant line 42 a such that the main refrigerant provides additional cooling to the air in evaporator 22. This operating mode is referred to as “Full loading with economizer” since valve 26 in economizer line 44 b is open and both cylinder modules 30 and 32 are operating at full capacity.

The economizer cycle is generally used when a ratio of discharge pressure to suction pressure in compressor 12 is high (typically when the system operates at pressure ratio above 3). As such, the pressure at the suction or inlet of compressor 12 is typically low, which is a function of low pressure inside evaporator 22. A low evaporator pressure typically correlates to a low ambient air temperature. In that case, refrigerant system 10 may operate in the economizer mode (i.e. valve 26 open) to further decrease the air temperature.

In the second mode shown in Table 1 and designated as “Mid-level unloading”, the economizer cycle is blocked by closing valve 26, which prevents refrigerant from circulating through economizer module 18. As such, refrigerant in the tapped refrigerant line essentially stops providing cooling to refrigerant in the main refrigerant line in economizer module 18. This mid-level unloading mode may commonly be used at low to moderate pressure ratio applications (typically in pressure ratio range from 1 to 3). When the air requiring cooling is at a high temperature, refrigerant system 10 provides higher cooling capacity when the economizer cycle is not active. A higher ambient air temperature commonly results in a high pressure in the evaporator. As such, a high ambient air temperature usually correlates to a low pressure ratio (discharge to suction). The pressure ratio may commonly be monitored or calculated to determine whether to engage or disengage the economizer cycle.

In the third mode of Table 1, labeled as “Full unloading A”, valve 24 is blocked such that the only refrigerant flowing through compressor 12 is the tapped refrigerant from economizer module 18. Because valve 26 is closed, refrigerant stops circulating through evaporator 22 and ceases to provide cooling to air passing through evaporator 22. This high level of unloading may be used when there is little to no cooling load required, yet it is desirable to continue operating refrigerant system 10, instead of completely shutting it down. By flowing the tapped refrigerant line from economizer module 18 through compressor 12, discharge cooling may be provided to compressor 12.

Finally, the last fourth mode shown in Table 1 and is designated as “Full unloading B” is a mode in which both valves 24 and 26 are closed. As such, the refrigerant stops circulating through refrigerant system 10 and is no longer able to provide cooling to air passing through evaporator 22. Similar to the “Full unloading A” mode above, refrigerant system 10 may operate in this mode when there is minimal, if any, cooling load present. It is recognized that this last mode is an unusual operating condition and additional steps may need to be taken to ensure that compressor 12, as well as other equipment in refrigerant system 10, does not overheat.

Valves 24 and 26 may be ON/OFF valves that have two positions—fully open and fully closed. This type of valve is typically a solenoid valve. Alternatively, either or both of valves 24 and 26 may be a variable opening valve or “stepper motor drive” valve. The stepper motor may position valves 24 and 26 at a fully open position, a fully closed position, and anywhere in between. In preferred embodiments, valves 24 and 26 have a variable opening, since this provides greater flexibility and additional stages of loading and unloading. It is recognized that variations of the four modes shown in Table 1 are possible by adjusting one or both of valves 24 and 26 at an intermediate position between open and closed. If the stepper motor valves are utilized then, for example, for modes three and four, valve 24 may not be fully closed and, in this case, refrigerant system 10 will not have a full unloading operation.

Operation of valves 24 and 26 may be controlled by controller 28, which determines a most effective mode of operation based on particular parameters inside refrigerant system 10. Depending on sensed parameters, controller 28 adjusts valves 24 and 26. In the case of solenoid valves, the adjustments may be either an ON or OFF position. For variable opening valves, controller 28 may adjust the valves from fully open, fully closed or an intermediate position. To determine an operating mode and hence a position of valves 24 and 26, parameters sensed and relayed to controller 28 may include, but are not limited to, a temperature inside evaporator 22, a set point temperature of the air to be conditioned, a pressure at an inlet of compressor 12 (i.e. suction pressure), and a pressure at an outlet of compressor 12 (i.e. discharge pressure).

System 10 includes various sensors that communicate with controller 28. As shown in FIG. 1, temperature sensor 50 may be associated with evaporator 22 for sensing a temperature (T1) in evaporator 22. It is recognized that sensor 50 may include more than one temperature sensor positioned at various locations at evaporator 22. Several pressure sensors are also included in refrigerant system 10. As described above, the ratio of discharge pressure to suction pressure for compressor 12 may be used to determine an operating mode of refrigerant system 10. The suction pressure usually correlates to the pressure of the refrigerant exiting evaporator 22 and may commonly be measured at suction inlet 34 of main refrigerant line 42 c. However, if valve 24 is closed, refrigerant is not able to flow through suction inlet 34. Therefore, first pressure sensor 52 may be included in main refrigerant line 42 c at a position upstream of first valve 24 to measure suction pressure (P1) of the main refrigerant. Second pressure sensor 54 may be located near first discharge outlet 38 of main cylinder module 30 to sense a discharge pressure (P2) of the main refrigerant exiting compressor 12. Pressure sensor 56 may also be located in economizer line 44 b to measure a pressure (P3) in economizer line 44 b; and pressure sensor 58 may be located near second discharge outlet 40 of economizer cylinder module 32 to measure a discharge pressure (P4) at the exit from economizer cylinder module 32. In some embodiments, suction pressure (P3) and discharge pressure (P4) of economizer cylinder module 32 may not be included in refrigerant system 10. Pressures (P3) and (P4) may be less significant than suction pressure (P1) and discharge pressure (P2) of main cylinder module 30, which are used to analyze conditions at evaporator 22.

Data from sensors 50, 52, 54, 56 and 58 include temperature (T1) and pressures (P1) through (P4), which are inputs to controller 28, as shown in FIG. 1. In addition, temperature sensor 60 may be used to measure an ambient air temperature (AT), which is also an input to controller 28. User input 62 may include a set point temperature (SPT) for the air to be cooled in evaporator 22. It is recognized that additional sensors and additional inputs to controller 28 not shown in FIG. 1, may be included in refrigerant system 10. Based on the various inputs to controller 28, controller 28 regulates a position of valves 24 and 26 such that refrigerant system 10 operates efficiently and avoids nuisance shutdowns.

In the exemplary embodiment shown in FIG. 1, refrigerant system 10 includes first valve 24 in main refrigerant line 42 c between evaporator 22 and compressor 12, and second valve 26 in economizer refrigerant line 44 b between economizer module 18 and compressor 12. In an alternative embodiment, a refrigerant system may include only one of valves 24 and 26, and in that case, the refrigerant system is configured to operate in two of the four operating modes shown in Table 1.

FIG. 2 is a schematic of refrigerant system 110, which is an alternative embodiment of refrigerant system 10 of FIG. 1. Similar to refrigerant system 10, refrigerant system 110 includes compressor 112, high pressure heat exchanger 114, first expansion device 116, economizer module 118, second expansion device 120, evaporator 122, first valve 124, second valve 126, controller 128, and variable frequency drive (VFD) 129. Refrigerant system 110 operates in a similar manner to refrigerant system 10 described above. Compressor 112 includes main cylinder module 130 and economizer cylinder module 132. Each cylinder module 130 and 132 has its own inlet leading to the module and outlet exiting the module, and one or both of cylinder modules 130 and 132 may include more than one cylinder and more than one cylinder module. As shown in FIG. 2, first valve 124 is installed in main refrigerant line 142 c between evaporator 122 and inlet 134 to main cylinder module 130; second valve 126 is installed in economizer refrigerant line 144 b between economizer module 18 and inlet 136 of economizer cylinder module 132. Unlike refrigerant system 10, refrigerant system 110 includes connector refrigerant line 170 located between main refrigerant line 142 c and economizer refrigerant line 144 b, and third valve 172 installed in connector refrigerant line 170. In preferred embodiments, valves 124, 126 and 172 have variable openings such that refrigerant system 110 has additional flexibility to position valves 124, 126 and 172 at an intermediate position between fully open and fully closed.

In refrigerant system 10 shown in FIG. 1, valves 24 and 26 provide flexibility in terms of controlling flow from evaporator 22 to main cylinder module 30 and from economizer module 18 to economizer cylinder module 32. However, it is not possible in refrigerant system 10 to redirect refrigerant from main refrigerant line 42 c to economizer refrigerant line 44 b, and vice versa. As such, refrigerant system 10 prevents the main refrigerant stream from flowing through economizer cylinder module 32 and the economizer stream from flowing through main cylinder module 30. Refrigerant system 110 overcomes these limitations by installing connector line 170 between main refrigerant line 142 c and economizer refrigerant line 144 b. Valve 172 in connector refrigerant line 170 is preferably a bi-directional valve such that refrigerant can flow in either direction between main refrigerant line 142 c and economizer refrigerant line 144 b. Therefore refrigerant system 110 offers additional flexibility and control in terms of loading and unloading.

Refrigerant system 110 is able to operate in eight different operating modes, based on a position of valves 124, 126 and 172. The operating modes are generally ordered from highest to lowest cooling capacity. For purposes of the description below, a higher level of unloading corresponds to a lower cooling capacity. Four of the eight operating modes shown in Table 2 for refrigerant system 110 are feasible in refrigerant system 10 of FIG. 1. As described further below, system 110 provides even greater flexibility and control for unloading, as compared to refrigerant system 10 of FIG. 1. Moreover, system 110 also provides for greater cooling capacity than system 10 when the economizer cycle is not being used.

TABLE 2 Operating First Second Third Mode Valve 124 Valve 126 Valve 172 Comments 1. Full loading with Open Open Closed High pressure ratio. This mode economizer also feasible in system 10 (see Table 1). Same as if there are no valves 2. Full loading Open Closed Open Low pressure ratio without economizer 3. Low to mid-level Open Open Open Flow from both economizer and unloading line through main line 4. Mid-level Open Closed Closed This mode also feasible for unloading refrigerant system 10 (see Table 1). 5. Mid-level Closed Closed Open Evaporator flow only unloading economized cylinder module 6. Mid to high level Closed Open Open Flow from both main and unloading economizer line through economized cylinder module 7. Full unloading Closed Open Closed Discharge flow cooling. This mode is also feasible for refrigerant system 10 (see Table 1). 8. Full unloading Closed Closed Closed This mode is also feasible for refrigerant system 10 (see Table 1).

Two “Full loading” operating modes are shown above in Table 2. First, the “Full loading with economizer” mode was described above in reference to refrigerant system 10. Since both valves 124 and 126 are open, and valve 172 is closed, this mode is the same as a system having no valves in lines 142 and 144. The second “Full loading” operating mode, referred to in Table 2 as “Full loading without economizer”, is not feasible for refrigerant system 10 and allows for increased loading (i.e. increased cooling capacity) when the economizer cycle is not being used for low pressure ratio operation.

As described above in reference to FIG. 1 and Table 1, it may not be efficient to use the economizer cycle under some conditions, such as at low pressure ratio operation. In this case, refrigerant system 110 achieves a greater cooling capacity than refrigerant system 10 when the economizer cycle is blocked. In the second mode referred to as “Full loading without economizer”, valve 126 is closed, and valves 124 and 172 are open. As such, a portion of refrigerant from evaporator 122 flows from main refrigerant line 142 c through connector refrigerant line 170 and into economizer cylinder module 132. The remaining refrigerant from evaporator 122 flows through main cylinder module 130. As such, main cylinder module 130 and economizer cylinder module 132 operate in parallel to compress the main refrigerant from evaporator 122. By using all of the cylinder modules in compressor 112, instead of only main cylinder module 130, refrigerant system 110 is able to circulate a greater amount of refrigerant through evaporator 122. This allows evaporator 122 to generate more cooling during those times when the economizer cycle is not being used, but a high cooling capacity is desired.

It is recognized that the level of unloading may be adjusted for any given mode based on a position of valves 124, 126 and 172, in those embodiments in which the valves have variable openings.

In operating mode three, designated as low to mid-level unloading, all three valves 124, 126 and 172 are open. As such, at least a portion of flow from economizer refrigerant line 144 b flows through connector refrigerant line 170 and is combined with main refrigerant in main refrigerant line 142 c. In this mode, a greater portion, if not all of the refrigerant, flows through main cylinder module 130, and economizer cylinder module 132 compresses a minimal amount of refrigerant. Due to a limited capacity of main cylinder module 130, less cooling is provided in evaporator 122 in this mode, as compared to a mode in which all refrigerant from economizer refrigerant line 144 b were flowing through economizer cylinder module 130.

For operating mode four, first valve 124 is open, and second valve 126 and third valve 172 are closed. This operating mode was also feasible in refrigerant system 10 and was described above as mid-level unloading in Table 1. The economizer cycle is blocked in operating mode four. Because valve 172 is closed and economizer cylinder module 132 is thus not used, operating mode four provides less cooling as compared to operating mode two (i.e. full loading without economizer), and is therefore designated as an unloading mode. Additional unloading may be accomplished by partially closing first valve 124.

In operating mode five valves 124 and 126 are closed, while third valve 172 in connector refrigerant line 170 is open. Since valve 126 is closed, the economizer cycle is blocked, similar to operating mode four. However, in operating mode five, because valve 124 is also closed, all refrigerant flowing through line 142 c from evaporator 122 is directed through connector refrigerant line 170 and into economizer cylinder module 132.

Similar to the mode above, in operating mode six, first valve 124 is closed and third valve 172 is open. However, in contrast to above, the economizer cycle is activated by opening second valve 126. Since valve 124 is closed, the main refrigerant from evaporator 122 is directed through economizer cylinder module 132 in addition to the economizer refrigerant flowing through economizer refrigerant line 144 b. In the final two operating modes seven and eight of Table 2, designated as full unloading, third valve 172 in connector refrigerant line 170 is closed. Therefore, these two operating modes are feasible in a refrigerant system without a connector line, like refrigerant system 10 of FIG. 1, and were described above. Operating modes seven and eight are not common; if refrigerant system 110 operates in either of these modes, typically it is temporary operating mode and is used to avoid shutting down refrigerant system 110. Either of modes seven and eight may be adjusted to mid-level unloading or even a low level unloading by only partially closing one of the valves designated as being closed in Table 2. For example, if valve 124 is partially closed in either operating mode seven or eight, system 110 may operate between a low and mid-level unloading, depending on a specific position of valve 124.

Controller 128 regulates a position of valves 124, 126 and 172 in order to operate refrigerant system 110 in an operating mode that aligns with the cooling load demands, while still operating efficiently and avoiding nuisance shutdowns. As described above in reference to controller 28 of refrigerant system 10, controller 128 controls a position of valves 124, 126 and 172 based on sensed parameters in refrigerant system 110. Similar to refrigerant system 10, refrigerant system 110 may include temperature sensors 150 and 160 for measuring, respectively, a temperature (T1) inside evaporator 122 and an ambient air temperature (AT). Refrigerant system 110 also includes pressure sensors 152, 154 and 156 and 158, which are located in similar locations to those shown in FIG. 1. Due to a presence of connector refrigerant line 170, refrigerant system 110 may also include pressure sensor 159 located closer to suction inlet 134 for measuring pressure (P5). Pressure sensors 156 and 159 may be helpful during those modes when valve 172 is open in order to monitor a flow of refrigerant being redirected either from economizer refrigerant line 144 b to main refrigerant line 142 c or vice versa. The inputs to controller 128, as shown in FIG. 2, may include evaporator temperature (T1) and the ambient temperature (AT), as well as pressures (P1) through (P5). It is recognized that additional sensors and inputs not shown in FIG. 2 may be included in refrigerant system 110.

In the exemplary embodiment shown in FIG. 2, refrigerant system 110 also includes variable frequency drive 129 (VFD), which is used to drive an electric motor of compressor 112 and vary the speed of the motor. Variable frequency drive 129 is controlled by controller 128. Although VFD 129 is not required in refrigerant system 110, it may be used for additional capacity control since the speed of the motor impacts the capacity of compressor 112. Other types of adjustable speed drives may also be used. A variable frequency drive may also be used in refrigerant system 10 of FIG. 1.

Through the use of valves 124, 126, 172 and connector refrigerant line 170, refrigerant system 110 provides superior flexibility during unloading, as well as the feasibility to achieve a greater cooling capacity when the economizer module is not being used. In the exemplary embodiment shown in FIG. 2, refrigerant system 110 includes both valves 124 and 126 in combination with connector refrigerant line 170 and valve 172. In alternative embodiments, valve 124 or valve 126 may be eliminated.

In the embodiments shown in FIGS. 1 and 2, economizer module 18 is a heat exchanger. FIG. 3 is an alternative embodiment in which economizer module 218 is a flash tank. In refrigerant systems 10 and 110 the refrigerant exiting the high pressure heat exchanger is split into two refrigerant streams prior to entering the economizer heat exchanger. In contrast, in economizer module 218 of FIG. 3, the single refrigerant stream from the high pressure heat exchanger passes through expansion device 219, where it is partially expanded to an intermediate pressure and temperature. As such, the refrigerant entering flash tank 218 is usually in a two-phase thermodynamic state. Inside flash tank 218, phase separation occurs and refrigerant vapor exits flash tank 218 through economizer refrigerant line 242, at which point it travels to the economizer cylinder module (not shown). Liquid refrigerant exits flash tank 218 through refrigerant line 244 and passes through expansion or float flow control device 221 before traveling to the evaporator (not shown). In those embodiments using a float flow control device, float flow control device 221 is configured to open when a liquid level in the flash tank reaches a predetermined level or provide a certain restriction to a refrigerant flow to maintain a desired refrigerant level. The refrigerant exiting flash tank 218 through refrigerant line 244 has low vapor and high liquid content, which enhances cooling capacity in the evaporator.

The refrigerant system and operating method described herein may easily be implemented into existing refrigerant systems. The refrigerant systems may include supermarket refrigerant systems, container refrigerant systems, truck/trailer refrigerant systems, rooftop air conditioning and heat pump refrigerant systems, and residential air conditioning refrigerant systems. The valves may be installed in existing refrigerant lines, and in some cases, a connector refrigerant line may also be added between the economizer refrigerant line and the main refrigerant line. The valves and connector refrigerant line described herein may also be incorporated into the design of new refrigerant systems.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 

1. A refrigerant system comprising: a high pressure heat exchanger configured to absorb heat from refrigerant as the refrigerant passes through the high pressure heat exchanger; an economizer module configured to receive a first refrigerant stream and a second refrigerant stream derived from the refrigerant exiting the high pressure heat exchanger; an evaporator configured to evaporate the first refrigerant stream; a first refrigerant line extending from the evaporator and configured to receive the first refrigerant stream; a second refrigerant line extending from the economizer module and configured to receive the second refrigerant stream; a reciprocating compressor comprising: a main cylinder module having a first inlet connected to the first refrigerant line and configured to receive the first refrigerant stream and direct the first refrigerant stream through the main cylinder module; and an economizer cylinder module having a second inlet connected to the second refrigerant line and configured to receive the second refrigerant stream and direct the second refrigerant stream through the economizer cylinder module; and a controller for controlling flow of at least one of the first refrigerant stream and the second refrigerant stream.
 2. The refrigerant system of claim 1 further comprising at least one of a first valve in the first refrigerant line to control flow of the first refrigerant stream into the reciprocating compressor and a second valve in the second refrigerant line to control flow of the second refrigerant stream into the reciprocating compressor.
 3. The refrigerant system of claim 2 further comprising: a connector refrigerant line between the first refrigerant line and the second refrigerant line and configured to perform at least one of bypassing at least a portion of the first refrigerant stream into the economizer cylinder module and bypassing the second refrigerant stream into the main cylinder module; and a valve in the connector refrigerant line to control at least one of the bypass of the first refrigerant stream into the economizer cylinder module and the bypass of the second refrigerant stream into the main cylinder module.
 4. The refrigerant system of claim 3 wherein the valve in the connector refrigerant line is located downstream of a valve in the second refrigerant line and upstream of a valve in the first refrigerant line.
 5. The refrigerant system of claim 4 wherein the controller is configured to at least partially close the valve in the second refrigerant line and at least partially open the valve in the connector refrigerant line such that at least a portion of the first refrigerant stream flows through the second refrigerant line and through the economizer cylinder module.
 6. The refrigerant system of claim 4 wherein the controller is configured to at least partially close the valve in the first refrigerant line such that the first refrigerant stream flows through the second refrigerant line and through the economizer cylinder module.
 7. The refrigerant system of claim 4 wherein the controller is configured to at least partially open the valves in the first and second refrigerant lines and at least partially open the valve in the connector refrigerant line such that a portion of the second refrigerant stream flows through the first refrigerant line and through the main cylinder module.
 8. A method of operating a refrigerant system configured to provide cooling using a refrigerant and including a high pressure heat exchanger, an economizer module, an evaporator, and a reciprocating compressor having a main cylinder module with a first inlet and a first outlet and an economizer cylinder module with a second inlet and a second outlet, the method comprising: flowing the refrigerant through the high pressure heat exchanger, the economizer module, the evaporator, and at least one of the main cylinder module and the economizer cylinder module, wherein the refrigerant exiting the economizer module is in a main refrigerant stream and an economizer refrigerant stream, and the main refrigerant stream flows through the evaporator; controlling a flow of the refrigerant into the main cylinder module of the reciprocating compressor at least in part as a function of an operating mode of the refrigerant system; and controlling a flow of refrigerant into the economizer cylinder module of the reciprocating compressor at least in part as a function of the operating mode.
 9. The method of claim 8 wherein the operating mode is a function of at least one of an ambient air temperature, a set point air temperature, a pressure at an inlet of the reciprocating compressor, and a pressure at an outlet of the reciprocating compressor.
 10. The method of claim 8 wherein controlling a flow of the refrigerant into the main cylinder module includes preventing the main refrigerant stream exiting the evaporator from entering the main cylinder module.
 11. The method of claim 10 further comprising: directing the main refrigerant stream exiting the evaporator through the economizer cylinder module.
 12. The method of claim 8 wherein controlling a flow of the refrigerant into the economizer cylinder module includes preventing the economizer refrigerant stream exiting the economizer module from entering the economizer cylinder module.
 13. The method of claim 12 further comprising: directing at least a portion of the main refrigerant stream exiting the evaporator through the economizer cylinder module.
 14. The method of claim 12 further comprising: directing the economizer refrigerant stream exiting the economizer module through the main cylinder module.
 15. The method of claim 8 wherein the refrigerant system comprises: a first refrigerant line connecting the evaporator to the first inlet of the main cylinder module of the reciprocating compressor; and a second refrigerant line connecting the economizer module to the second inlet of the economizer cylinder module.
 16. The method of claim 15 wherein the refrigerant system further comprises: a connector refrigerant line between the first refrigerant line and the second refrigerant line; and a valve in the connector refrigerant line.
 17. The method of claim 16 wherein the refrigerant system further comprises: a first valve in the first refrigerant line; and a second valve in the second refrigerant line, wherein the valve in the connector refrigerant line is located downstream of the second valve and upstream of the first valve.
 18. A method of controlling a refrigerant system configured to circulate a refrigerant and including a high pressure heat exchanger, an economizer module, an evaporator, a reciprocating compressor having a first inlet and a second inlet and configured to receive two separate refrigerant streams, a first refrigerant line between the evaporator and the first inlet of the reciprocating compressor, and a second refrigerant line between the economizer module and the second inlet of the reciprocating compressor, the method comprising: monitoring at least one of an ambient air temperature, a set point air temperature, a pressure at an inlet of the reciprocating compressor, and a pressure at an outlet of the reciprocating compressor to determine an operating mode of the refrigerant system; regulating flow of the refrigerant through the first refrigerant line and into the main cylinder module at least in part as a function of the operating mode; and regulating flow of the refrigerant through the second refrigerant line and into the economizer cylinder module at least in part as a function of the operating mode.
 19. The method of claim 18 further comprising: regulating flow of the refrigerant between the first refrigerant line and the second refrigerant line.
 20. The method of claim 19 wherein regulating flow of the refrigerant through the second refrigerant line includes directing at least a portion of the refrigerant from the evaporator into the economizer cylinder module. 